An analysis of a nitrogen-induced depression of yield in irrigated 'Kopara' wheat

Heavy applications of nitrogen fertiliser (200 kg/ha) applied in early spring to wheat (Triticum aestivum L. cv. 'Kopara') on a Wakanui silt loam, in which irrigation was used to maintain soil-water levels above -0.5 bar, depressed grain yield by 30%. Poor grain set was the main cause of the low yields, but mean grain weights were also reduced. Analysis of data indicated that grain set was probably restricted by the availability of carbohydrate during the critical pre-anthesis period of floret development

An analysis of a wheat yield depression caused by high sowing rate with reference to the pattern of grain set within the ear

Grain set in spikelets of ears was reduced in spring-sown wheat established at high sowing rate (500 viable seeds/m²) compared with wheat planted at normal rates (250 seeds/m²), the reduction being greatest in spikelets positioned near the base and near the apex of the ear. Regression analysis revealed a significant and positive relationship between final grain set and spikelet dry weight at the early boot stage. Poor grain set in wheat grown at supra-optimal seeding rates was attributed to a combination of reduced carbohydrate supply and water stress in the young developing ear

Development and yield components of high-yielding wheat crops

In a field experiment, 'Arawa' wheat outyielded 'Aotea' by 10% through the production of a higher grain yield per ear. Irrigation had no effect on grain yield because of plant uptake of subsoil moisture. Nitrogen increased grain yield by 19% mainly by increasing ear number. Sowing rate had no effect on yield. Mean yield for the experiment was 6.6 t/ha, the mean yield components being 600 ears/m², each composed of just over 17 spikelets containing 1.5 grains which weighed 43 mg. Arawa produced larger grain than Aotea; no other treatment influenced mean weight per grain, which was unrelated to flag-leaf-area duration. It is suggested that further yield increases will best be achieved by increasing grain number per unit area, probably by increasing grains per spikelet, the component most highly correlated with yield in this experiment

Dynamics of tiller populations of standard height and semi-dwarf wheats

The effects of sowing rate and N fertiliser on tiller populations in field-sown wheat were investigated. Two cultivars were evaluated, a semi-dwarf wheat cv. “Karamu” and a standard height wheat cv. “Kopara”. The number of tillers represented in a population was related to their order of appearance, namely: main stem, Tiller 1, Tiller 2, Tiller 3, Tiller 4, and secondary tillers. The maximum rate of tiller production in the semi-dwarf exceeded 450 tillers/m²/week whereas the standard height wheat reached a rate of 390 tillers/m²/week. Kopara produced more tillers than the semi-dwarf but fewer survived to maturity. Maximum tiller death rates of the standard wheat exceeded 300 tillers/m²/week whereas tiller senescence was 210 tillers/m²/week in the semi-dwarf. Tiller numbers per plant were fewer at 500 plants/m², but the increased proportion of main stems at the higher seeding rate resulted in a higher spike population because of their low mortality rate. N fertiliser at 90 kg/ha increased tiller numbers in a similar manner to a low seeding rate with Tiller 3 showing the greatest response. Tiller survival to harvest was also increased by application of N fertiliser. Tillers in Kopara were more likely to succumb to stress

A multi-instrument view of tail reconnection at Saturn

Three instances of tail reconnection events at Saturn involving the ejection of plasmoids downtail have been reported by Jackman et al. (2007) using data from Cassini’s magnetometer (MAG). Here we show two newly discovered events, as identified in the MAG data by northward/southward turnings and intensifications of the field. We discuss these events along with the original three, with the added benefit of plasma and energetic particle data. The northward/southward turnings of the field elucidate the position of the spacecraft relative to the reconnection point and passing plasmoids, while the variability of the azimuthal and radial field components during these events indicates corresponding changes in the angular momentum of the magnetotail plasma following reconnection. Other observable effects include a reversal in flow direction of energetic particles, and the apparent evacuation of the plasma sheet following the passage of plasmoids